This application claims the priority of German Patent Document 198 41 619.9, filed Sep. 11, 1998, published Mar. 23, 2000, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a material wire for producing wear-resistant and tribologically favorable surface coatings from supereutectic Al/Si alloys by thermal spraying.
Coatings of Al/Si alloys are known. In particular, such coating are used as cylinder running surfaces of cylinder housings of reciprocating piston engines. Coatings of Al/Si alloys are known, for example, from U.S. Pat. No. 5,022,455. Molten aluminum and silicon particles are sprayed separately onto the surface to be coated. Other Al/Si alloys are known, for example, from DE 40 20 268 C1; U.S. Pat. No. 4,711,823; U.S. Pat. No. 4,737,206; U.S. Pat. No. 4,969,428; and DE 44 38 550 A1. Another alloy is known from U.S. Pat. No. 4,959,276.
Coatings of this kind can be applied in many different ways to the surfaces of substrates. Thermal spraying, such as wire arc spraying or plasma spraying, are especially suitable. In plasma spraying, powdered starting material melted in a flame is used. In wire arc spraying, a metal starting material in the form of a material wire is used. Wire arc spraying is especially preferred because it permits a high application rate of the coating by high cycles and is economical in terms of both the material and the system.
A composite material wire is disclosed in DE 43 41 537 A1 for wire arc spraying as well as a method for its manufacture. The wire has a solid core made of conducting metal and a jacket in which solid lubricant particles and wear-resistant particles are suspended homogeneously in a conducting metal that corresponds to the solid core. A composite wire of this kind, however, is relatively costly to manufacture and is not suitable for all applications.
The object of the present invention is to produce a material wire that can be manufactured simply and economically and that permits the production of surface coatings from a supereutectic Al/Si alloys.
This object is achieved by a material wire that is a filler wire having a jacket made of metallic aluminum and a filling made of one or more alloy components.
The alloy components (i.e., the starting materials for making the desired Al/Si alloy) are used for producing the wire. The hollow aluminum jacket remains unchanged and the filling is put together individually depending on the composition required in the desired Al/Si alloy. The individual components combine during melting in wire arc spraying and during application to the surface of the actual alloy. In this fashion, a material wire is produced that can be manufactured simply and economically and which can be used to make any Al/Si alloy.
One especially preferred embodiment of the material wire according to the present invention contains silicon in the filling as well as nickel, iron, magnesium, copper, cobalt, chromium, manganese, tin, zinc, zirconium and/or additional alloy components. The quantity of silicon in the filling is such that the resultant alloy contains about 17-40 wt. % silicon.
Another advantageous embodiment consists in the fact that the filling, in addition to the other alloy components, also contains additional additives, for example, hard metal particles, ceramic particles, or dry lubricants.
The material wire according to the present invention is preferably processed to form an aluminum-silicon alloy which is essentially copper-free, in other words it contains less than 1 wt. % copper.
The material wire according to the present invention is especially suited for making cylinder running surfaces in internal combustion engines. It is especially suitable for making coatings like those known from unpublished German Patent Application 197 33 208.8-45, filed on Aug. 1, 1997. These coatings consist essentially of a supereutectic aluminum-silicon alloy or an aluminum-silicon composite marked by a heterogeneous layer structure of aluminum-mixed crystal; a coarse to very fine network of eutectic silicon, silicon precipitates or particles; intermetallic phases; and extremely finely distributed oxides. These coatings have characteristic primary aluminum-mixed crystal dendrites in which the dendrite arms are sheathed in eutectic silicon. The polished sections of such coatings show a characteristic spongy appearance. Silicon-primary precipitates and silicon particles are present in only small quantities and have a small diameter. During the surface treatment of these layers, the dendrite arms that lie on the surface are polished so that during subsequent exposure the aluminum is etched away and aluminum-free silicon structures remain that form the actual running surface.
The material wire according to the present invention is especially suited for wire arc spraying but also for high-speed flame spraying (HVOF).
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.